Fix CVE-2018-1060:
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-1060

Taken from upstream commit (sans test and NEWS):
https://github.com/python/cpython/commit/e052d40cea15f582b50947f7d906b39744dc62a2

diff --git a/Lib/poplib.py b/Lib/poplib.py
index b91e5f72d2ca..a238510b38fc 100644
--- a/Lib/poplib.py
+++ b/Lib/poplib.py
@@ -274,7 +274,7 @@ def rpop(self, user):
         return self._shortcmd('RPOP %s' % user)
 
 
-    timestamp = re.compile(r'\+OK.*(<[^>]+>)')
+    timestamp = re.compile(br'\+OK.[^<]*(<.*>)')
 
     def apop(self, user, secret):
         """Authorisation

